Revenues from Contracts with Customers (Schedule of Components of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Feb. 28, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 569,987	$ 728,416
Revenue from other sources	625,025	432,695
Total revenues	1,195,012	1,161,111
Commissions and other fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	147,134	147,902
Total revenues	147,134	147,902
Investment banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	285,596	439,991
Total revenues	285,596	439,991
Manufacturing revenues
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	75,425	98,365
Total revenues	75,425	98,365
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	61,832	42,158
Principal transactions
Disaggregation of Revenue [Line Items]
Revenue from other sources	246,182	145,663
Total revenues	246,182	145,663
Interest income
Disaggregation of Revenue [Line Items]
Revenue from other sources	386,844	275,222
Total revenues	386,844	275,222
Other
Disaggregation of Revenue [Line Items]
Revenue from other sources	$ (8,001)	$ 11,810